The Hammersmith and City line is one of the lines affected

Drivers will stage 24-hour walkouts on Christmas Eve and New Year's Eve over the "unfair" sacking of a colleague.

The man, seen leaving a squash court while on sick leave, maintained he was exercising to aid his return to work.

A similar strike last month closed the Circle Line, which is normally used by 230,000 passengers a day.

And only a limited number of trains ran on the Hammersmith & City line, which carries 162,000 people daily.

The Rail, Maritime and Transport (RMT) union general secretary, Bob Crow, said London Underground (LU) had failed to reverse the sacking and workers were fully behind the driver.

We are surprised the RMT are taking action as Londoners try to enjoy their Christmas and New Year London Underground

But he said the union was prepared to hold talks at the conciliation service Acas.

"We can't allow for injustices when our member was quite clearly told he needed sports therapy to repair his ankle," he told BBC London at the time of the previous strike.

LU said it was "surprised" the RMT was taking more action, "especially as Londoners try to enjoy their Christmas and New Year".

In a statement, it said: "This employee has exhausted the appeals process and we believe his dismissal was both appropriate and fair."

It promised to provide the best service possible on the strike days.

Mayor Ken Livingstone has already been accused by the RMT of inflaming the row by supporting the sacking and claiming the driver had been off sick 20% of the time since he started working on the underground in 1998.

"I am only surprised he was allowed to get away with it for so long," he said.

The RMT says drivers will not clock on for shifts starting between 0430 GMT on 24 December and 0429 GMT on 25 December, and between noon on 31 December and 1159 GMT on 1 January, 2004.

This means Tube services will be disrupted during the first part of New Year's Day.